Positron emission tomograph

ABSTRACT

In a PET apparatus  1,  in a calculation processing unit  50,  for each frame, radiation data for a region of interest K of a measurement-subjected part H is extracted, and then the optimum administration rate of a labeled substance T is calculated based on the radiation data such that the radiation concentration for the region of interest K will be steady regardless of the physiological state (blood flow rate etc.) of the subject S. In an administration rate control unit  60,  feedback control of the administration rate of the labeled substance into the subject S is carried out based on the calculated optimum administration condition. As a result, the change in the amount accumulated of the labeled substance T in the region of interest K between before and after administration of a drug being tested Y can be obtained easily and precisely in real time as the amount of change in the radiation concentration, and it becomes possible to grasp the measurement results rapidly and easily.

TECHNICAL FIELD

[0001] The present invention relates to a positron emission tomographyapparatus that can be suitably used for example in the evaluation of adrug being tested.

BACKGROUND ART

[0002] With a positron emission tomography apparatus (hereinafterreferred to as ‘PET apparatus’), a positron-emitting labeled substanceis administered into a subject, and also coincidence counting is carriedout of radiation generated in a measurement-subjected part of thesubject accompanying electron-positron pair annihilation, and thespatial distribution of the radiation concentration in themeasurement-subjected part is measured and made into an image, and hencefor example changes in the amount accumulated of the labeled substancein a specific region of interest of the measurement-subjected part arestudied; PET apparatuses are being applied to the evaluation of drugsfor Alzheimer-type or vascular-type dementia and so on.

[0003]FIG. 10 is a block diagram showing the constitution of aconventional PET apparatus. The PET apparatus 100 has a detection unit101, a data collection unit 102, an image reconstruction unit 103, andan intravenous injection unit 104. Here, the data collection unit 102has a frame-dependent histogram count memory 105.

[0004] A description will now be given of the operation of this PETapparatus 100. Firstly, a labeled substance T is intravenously injectedinto a subject S (for example a monkey) using the intravenous injectionunit 104. Next, the measurement-subjected part H (for example the head)of the subject S is inserted into a measurement space within thedetection unit 101, and then coincidence counting of radiation emittedby the labeled substance T that has reached the head of the subject S iscarried out by the detection unit 101, and the coincidence count data istransmitted to the data collection unit 102. In the data collection unit102, the transmitted coincidence count data is accumulated in theframe-dependent histogram count memory 105, and is summed in accordancewith the image frame. The summed data is then sent to the imagereconstruction unit 103, and based on this the radiation concentrationdistribution in the measurement-subjected part H of the subject S ismade into an image.

[0005] In a drug evaluation test, after the labeled substance T has beenadministered, the drug being tested Y is administered to the subject S.Then, by carrying out numerical analysis of the radiation concentrationsobtained as described above based on physiological constantscharacteristic of the subject S and so on, the change and so on in theaccumulated amount of the labeled substance T in a region of interest ofthe measurement-subjected part H between before and after theadministration of the drug being tested Y is obtained.

DISCLOSURE OF THE INVENTION

[0006] With a conventional PET apparatus, in general a method is used inwhich the labeled substance is injected through a single intravenousinjection (the so-called bolus injection method).

[0007] However, with this bolus injection method, the S/N ratio dropsduring the latter half of the measurements due to the half life of thelabeled substance, and hence to compensate for this the amountadministered of the labeled substance must be set rather high.Consequently, the radiation exposure dose to the subject becomes high,and moreover it is necessary to make the radiation concentrationmeasurement range of the PET apparatus broad so that radiationconcentrations from the high radiation concentrations at the start ofthe measurements to the low radiation concentrations during the latterhalf of the measurements can be measured.

[0008] On the other hand, with conventional PET apparatuses, instead ofthe bolus injection method, a method has also been used in which thesubject is made to continuously inhale a gas containing the labeledsubstance at a steady rate (the so-called steady gas inhalation method).The aim of this steady gas inhalation method is to make the radiationconcentration in the subject be in a steady state.

[0009] However, with this steady gas inhalation method, the flow rateand so on of the labeled substance is greatly affected by changes in thephysiological state (in particular the respiration rate) of the subject,and hence in actual practice it is difficult to make the radiationconcentration in the subject be in a steady state. Many errors are thuscontained in the measured radiation concentrations, and the experimentalaccuracy cannot be guaranteed.

[0010] Moreover, with a conventional PET apparatus, to carry out thenumerical analysis on the measured data, it is necessary to gain anunderstanding of the state of the bodily functions (for example theradiation concentration in the blood) of the subject during theexperiment. A sample of arterial blood is thus taken from the subjectduring or after the experiment, this arterial blood is analyzed, and aphysiological constant that indicates the state in the subject duringthe experiment is calculated.

[0011] However, taking a sample of arterial blood imposes physical andpsychological burdens on the subject, and in addition specialist staffare separately required for taking the blood sample, and furthermorethere is a risk of these staff being exposed to radiation from thesampled blood. Moreover, a great deal of staff and expensive equipment(chromatography equipment, auto gamma counter etc.) are required foranalyzing the sampled blood.

[0012] Furthermore, to carry out numerical analysis using thephysiological constant obtained as described above, it is necessary tocarry out complex analytical calculations including convolutionintegrals. Staff and calculating equipment for the numerical analysisare thus separately required, and it may take a long time (e.g. 1 week)until the results are ascertained. In such a case, it is not possible tochange the conditions of the next experiment as appropriate based on theresults of the immediately preceding experiment, which leads toconsiderable delays in the progress of the experiments.

[0013] In view of the above problems, it is an object of the presentinvention to provide a positron emission tomography apparatus (PETapparatus) that enables measurements to be carried out easily andprecisely, and also enables measurement results to be grasped rapidlyand easily.

[0014] The positron emission tomography apparatus (PET apparatus)according to the present invention, which is a PET apparatus thatadministers a positron-emitting labeled substance into a subject, andalso carries out coincidence counting of radiation generated in ameasurement-subjected part of the subject accompanying electron-positronpair annihilation, and measures the spatial distribution of theradiation concentration in the measurement-subjected part, ischaracterized by having region-of-interest data extraction means forextracting radiation data for a specified region of interest from out ofthe radiation data that has been obtained by coincidence counting fromthe measurement-subjected part, administration condition calculationmeans for calculating an optimum administration condition for thelabeled substance into the subject based on the extracted radiation datafor the region of interest, and administration control means forcarrying out feedback control of an administration condition for thelabeled substance into the subject based on the optimum administrationcondition.

[0015] According to this PET apparatus, radiation data for a region ofinterest of the measurement-subjected part is extracted for example foreach frame, and then an optimum administration condition (e.g. amountadministered per unit time) for the labeled substance such that theradiation concentration for the region of interest becomes steadyregardless of the physiological state (blood flow rate etc.) of thesubject is calculated based on the radiation data, and feedback controlis carried out of the amount administered or the like of the labeledsubstance to the subject in accordance with the optimum administrationcondition.

[0016] If, in this way, feedback control is carried out such that theradiation concentration for the region of interest—not the radiationconcentration for the whole of the measurement-subjected part—becomessteady, then there is no longer any need to broaden the radiationconcentration measurement range of the PET apparatus. Moreover, itbecomes possible to obtain the change in the amount accumulated of thelabeled substance in the region of interest between before and afteradministration of a drug being tested easily and precisely in real timeas the amount of change in the radiation concentration. Sampling ofarterial blood and complex numerical calculations are thus unnecessary,and hence great cutbacks can be made in the staff, time, analyticalequipment and so on required for calculating the experimental results.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a block diagram showing the constitution of a PETapparatus according to a first embodiment;

[0018]FIG. 2 is a flowchart explaining region-of-interest dataextraction processing, administration rate calculation processing andadministration rate control processing in the PET apparatus according tothe first embodiment;

[0019]FIG. 3 is a schematic drawing for explaining extraction ofradiation data for the region of interest in the PET apparatus accordingto the first embodiment;

[0020]FIG. 4 is a detailed flowchart explaining the administration ratecalculation processing in the PET apparatus according to the firstembodiment;

[0021]FIG. 5 is a graph showing the changes over time in the radiationconcentration for the region of interest in the case of the PETapparatus according to the first embodiment;

[0022]FIG. 6 is a flowchart explaining region-of-interest dataextraction processing and administration rate control processing in aPET apparatus according to a second embodiment;

[0023]FIG. 7 is a schematic drawing for explaining extraction ofradiation data for the region of interest in the PET apparatus accordingto the second embodiment;

[0024]FIG. 8 is a flowchart explaining region-of-interest dataextraction processing and administration rate control processing in aPET apparatus according to a third embodiment;

[0025]FIG. 9 is a schematic drawing for explaining the calculation ofdetector pair contribution rates in the PET apparatus according to thethird embodiment; and

[0026]FIG. 10 is a block diagram showing the constitution of aconventional PET apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Following is a detailed description of embodiments of thepositron emission tomography apparatus (PET apparatus) according to thepresent invention, with reference to the accompanying drawings. Notethat identical or corresponding elements are represented by the samereference numeral, and redundant repeated description is omitted.

[0028] Firstly, a description will be given of a first embodiment of thepositron emission tomography apparatus (PET apparatus) according to thepresent invention. FIG. 1 is a block diagram of the constitution of thePET apparatus 1 according to the first embodiment. As shown in FIG. 1,the PET apparatus 1 comprises a detection unit 10, a data collectionunit 20, an image information control unit 30, an intravenous injectionunit 40, a calculation processing unit 50, an administration ratecontrol unit 60, and a display unit 70.

[0029] The detection unit 10 has contained therein a measurement spaceinto which a measurement-subjected part (for example the head) H of asubject (for example a monkey) S can be placed, and a large number ofdetectors are arranged in a ring around the central axis. For each ofthese detectors, the ray-receiving surface faces into the measurementspace, and hence the detector detects radiation emitted from themeasurement space side. Each of the detectors of the detection unit 10is connected to the data collection unit 20 by a signal line, anddetection signals that depend on the energy of the detected radiationare transmitted from the detectors to the data collection unit 20.

[0030] The data collection unit 20 has an imaged-frame-dependenthistogram memory 21 and an imaged-frame-independent histogram memory 22.The data collection unit 20 recognizes when a pair of detectors out ofthe large number of detectors constituting the detection unit 10 havesimultaneously detected radiation (energy 511 keV) generatedaccompanying electron-positron pair annihilation based on the detectionsignals transmitted from the detection unit 10, and stores thecoincidence count data based on the detection signals in theimaged-frame-dependent histogram memory 21 and theimaged-frame-independent histogram memory 22.

[0031] The imaged-frame-dependent histogram memory 21 is connected tothe image information control unit 30 by a signal line. Moreover, theimaged-frame-independent histogram memory 22 is connected to thecalculation processing unit 50 by a signal line. The data accumulatedand summed in the imaged-frame-dependent histogram memory 21 istransmitted to the image information control unit 30 in accordance withthe imaged frames (time periods that act to delimit the datacollection), which are preset.

[0032] The image information control unit 30 has an image informationmemory 31, and information such as a mask image created in advancebefore commencing measurement is stored in this image information memory31. The image information control unit 30 is connected to thecalculation processing unit 50 by a signal line, and image informationand so on stored in the image information memory 31 is transmitted tothe calculation processing unit 50 in accordance with the imaged framesand so on.

[0033] The intravenous injection unit 40 has an injection needle forcarrying out intravenous injection into the subject S, and a pump or thelike for injecting the labeled substance T into the subject S. Duringthe measurement period, the injection needle is kept in a state insertedinto the subject S, and the labeled substance T is continuouslyadministered using the pump. Moreover, the pump has a structure suchthat it is possible to change the rate of intravenous injection of thelabeled substance T upon receiving control from the administration ratecontrol unit 60, which is the administration control means.

[0034] The calculation processing unit 50 extracts radiation data for aspecified region of interest K in the measurement-subjected part H basedon the coincidence count data transmitted from theimaged-frame-independent histogram memory 22 and the image informationtransmitted from the image information control unit 30 and so on, andcalculates the radiation concentration for the region of interest K andthe optimum administration rate (intravenously injected amount per unittime). The calculation processing unit 50 is connected to theadministration rate control unit 60 and the display unit 70 by signallines; the calculated radiation concentration for the region of interestK is transmitted to the display unit 70, and the calculated optimumadministration rate is transmitted to the administration rate controlunit 60.

[0035] The administration rate control unit 60 is connected to theintravenous injection unit 40 by a signal line, and controls the rate ofadministration by the intravenous injection unit 40 based on thetransmitted optimum administration rate information. Moreover, thedisplay unit 70 is a liquid crystal monitor or the like, and displaysthe transmitted radiation concentration for the region of interest K asa graph or the like.

[0036] Next, a description will be given of the operation of the PETapparatus 1 according to the present embodiment with reference to theflowchart shown in FIG. 2, focusing in particular on theregion-of-interest data extraction processing, the administration ratecalculation processing (administration condition calculation processing)and the administration rate control processing (administration controlprocessing).

[0037] Before describing the processing carried out after commencingmeasurement, a description will be given of processing carried outbefore commencing measurement. In this pre-measurement processing,firstly an MRI anatomical image or the like of the measurement-subjectedpart H of the subject S that has been measured in advance is inputtedinto the image in formation memory 31 of the image information controlunit 30 (step 1-1; hereinafter steps are abbreviated to ‘S1-1’ and soon). Next, the region of interest K is set on this image (S1-2). Theregion of interest K is a part where the amount accumulated or the likeof the labeled substance T changes through the administration of thedrug being tested Y, and is selected as appropriate in accordance withthe type of the drug being tested Y, the objective and so on.

[0038] Next, a mask image that leaves behind only the data for theregion of interest K is created based on the set image (S1-3). In thismask image, 1 is set within the region of interest K, and 0 is set inthe region other than the region of interest K. After the mask image hasbeen created, alignment of the mask image and the PET image is carriedout (S1-4).

[0039] After the pre-measurement processing has been carried out asdescribed above, measurement is commenced. The measurement-subjectedpart H of the subject S is inserted into the measurement space of thedetection unit 10, and administration of the labeled substance T (forexample a compound containing positron-emitting ¹⁵O or the like) intothe subject S is commenced. Coincidence counting of the radiationgenerated from the measurement-subjected part H due to electron-positronpair annihilation is then carried out, and the coincidence count data iscollected in the imaged-frame-dependent histogram memory 21 and theimaged-frame-independent histogram memory 22 (S1-11). The coincidencecount data is collected repeatedly until one frame has been completed,with the coincidence count data being accumulated in theimaged-frame-dependent histogram memory 21 and theimaged-frame-independent histogram memory 22.

[0040] Once the frame has been completed, the summed coincidence countdata is transmitted to the calculation processing unit 50, andreconstruction of the PET image (radiation data image) of themeasurement-subjected part H is carried out based on the coincidencecount data (S1-12). At this time, the pre-aligned mask image istransmitted from the image information control unit 30 to thecalculation processing unit 50. The reconstructed PET image and the maskimage are then composited in the calculation processing unit 50 (S1-13).Through this composition, the PET image for the region of interest K(i.e. an image that shows the radiation concentration distributionwithin the region of interest) is extracted, for example as shown inFIG. 3.

[0041] Next, in the calculation processing unit 50, PET data (radiationconcentration data) for the region of interest K is obtained based onthe extracted PET image for the region of interest K (S1-14). This PETdata for the region of interest K is transmitted to the display unit 70,and is displayed as a graph or the like. Moreover, in the calculationprocessing unit 50, the optimum administration rate such that theradiation concentration for the region of interest K will be steady iscalculated based on the PET data for the region of interest K (S1-15).

[0042] Here, the processing to calculate the optimum administration rate(optimum administration condition) will be described in detail withreference to the flowchart shown in FIG. 4. As pre-processing whencarrying out this calculation processing, past PET data is inputted intothe image information memory 31 of the image information control unit 30in advance (S1-21). Out of the inputted PET data, input function datathat one wishes to take as a reference is then preset (S1-22), and areference input function graph is created based on this reference inputfunction data (S1-23).

[0043] After the PET data for the region of interest K has beencalculated in S1-14, the deviation between the reference input functiongraph that has been created in advance and the graph from the calculatedPET data is calculated (S1-24). The optimum administration rate of thelabeled substance T for correcting this deviation is then calculated(S1-25). Note that the graph from the PET data obtained for this framemay be substituted for the preset reference input function graph, andused as the reference input function graph for the next frame.

[0044] Afterwards, information on the calculated optimum administrationrate is transmitted to the administration rate control unit 60, and theadministration rate control unit 60 carries out feedback control suchthat the administration rate (administration condition) of the labeledsubstance T in the intravenous injection unit 40 becomes the optimumadministration rate (S1-16). Once the above sequence of processing hasbeen completed, the measurement progresses to the next frame. During themeasurement for the next frame, the intravenous injection unit 40administers the labeled substance T to the subject S at the calculatedoptimum administration rate.

[0045] The above processing is repeated, progressing from frame toframe. Because feedback control of the administration rate is carriedout for each frame, as the frames are progressed through, the radiationconcentration generated from the region of interest K becomes steady.The drug being tested Y is administered to the subject S after theradiation concentration generated from the region of interest K hasreached a steady state. The drug being tested Y is then evaluated byobserving the change in the radiation concentration generated from theregion of interest K (i.e. the change in the amount accumulated of thelabeled substance T).

[0046]FIG. 5 is a graph showing the changes over time in the radiationconcentration for the region of interest in the case of the PETapparatus according to the present embodiment; such a graph can bevisually checked in real time on the display unit 70. As shown in FIG.5, the changes over time in the radiation concentration generated fromthe region of interest K can broadly be divided into 3 periods.

[0047] The first period P1 is a stage when the radiation concentrationfor the region of interest K is still not stable, depending on the bloodflow rate and so on. The second period P2 is a stage when, due tofeedback control of the administration rate of the labeled substance Thaving been carried out, the radiation concentration for the region ofinterest K has reached a steady state. The third period P3 is a stagewhen changes have arisen in the radiation concentration for the regionof interest K, which had been in a steady state, due to administrationof the drug being tested Y. In the present embodiment, the effect of thedrug being tested Y is evaluated by studying the changes in theradiation concentration for the region of interest K during the periodP3.

[0048] According to the PET apparatus 1 of the present embodiment, foreach frame, after the coincidence count data for the region of interestof the measurement-subjected part has been extracted, the optimumadministration rate of the labeled substance such that the radiationconcentration for the region of interest K will be steady regardless ofthe physiological state (blood flow rate etc.) of the subject S iscalculated as an optimum administration condition, this being based onthe radiation concentration data for the region of interest K obtainedfrom the coincidence count data. Feedback control of the administrationrate of the labeled substance T to the subject S is then carried outbased on the calculated optimum administration rate.

[0049] If, in this way, feedback control is carried out such that theradiation concentration for the region of interest K—not the radiationconcentration for the whole of the measurement-subjected part H—becomessteady, then there is no longer any need to broaden the radiationconcentration measurement range. Moreover, it becomes possible to obtainthe change in the amount accumulated of the labeled substance T in theregion of interest K between before and after administration of the drugbeing tested Y easily and precisely in real time as the amount of changein the radiation concentration. Sampling of arterial blood and complexnumerical analysis are thus unnecessary, and hence great cutbacks can bemade in the staff, time, analytical equipment and so on required forcalculating the experimental results.

[0050] Moreover, with the PET apparatus 1 according to the presentembodiment, the extracted radiation concentration data is displayed inreal time on the display unit 70 as a graph or the like. It thus becomespossible to visually check changes and so on in the radiationconcentration for the region of interest K easily in real time, andhence the measurement results and so on can be judged rapidly.

[0051] Moreover, with the PET apparatus 1 according to the presentembodiment, by extracting the radiation data for the region of interestas an image, the accuracy of the extraction can be raised, and inaddition the extraction can be carried out as radiation concentrations,not as coincidence count data.

[0052] Furthermore, with the PET apparatus 1 according to the presentembodiment, a reference input function graph is created in advance, andthe administration rate of the labeled substance T such as to correctthe deviation from the reference input function graph is calculated.There is thus no longer any need to carry out complex calculations oranalysis not only in the case that measurements are carried out aplurality of times on the same subject, but even in the case thatmeasurements are carried out on a plurality of subjects (i.e. subjectshaving different physiological constants).

[0053] Next, a description will be given of a second embodiment of thepositron emission tomography apparatus (PET apparatus) according to thepresent invention. The constitution of the PET apparatus 2 according tothe second embodiment is very similar to that of the first embodiment,and hence here a description will be given of the operation of the PETapparatus 2 with reference to the flowchart shown in FIG. 6, focusing inparticular on the region-of-interest data extraction processing, theadministration rate calculation processing and the administration ratecontrol processing.

[0054] Before describing the processing carried out after commencingmeasurement, a description will be given of processing carried outbefore commencing measurement. In this pre-measurement processing, as inthe first embodiment, an MRI anatomical image or the like of themeasurement-subjected part H of the subject S that has been measured inadvance is inputted into the image information memory 31 of the imageinformation control unit 30 (S2-1), and then the region of interest K isset on this image (S2-2).

[0055] Next, a mask image that leaves behind only the data for theregion of interest K is created based on the set image (S2-3), and thenalignment of the mask image and the PET image is carried out (S2-4).After this, in the present embodiment, forward projection of the maskimage onto projection data is carried out, thus creating a projectedmask (S2-5).

[0056] After the pre-measurement processing has been carried out asdescribed above, measurement is commenced. The measurement-subjectedpart H of the subject S is inserted into the measurement space of thedetection unit 10, and administration of the labeled substance T intothe subject S is commenced. Coincidence counting of the radiationgenerated from the measurement-subjected part is then carried out, andthe coincidence count data is collected in the imaged-frame-dependenthistogram memory 21 and the imaged-frame-independent histogram memory 22(S2-11). The coincidence count data is collected repeatedly until oneframe has been completed, with the coincidence count data beingaccumulated in the imaged-frame-dependent histogram memory 21 and theimaged-frame-independent histogram memory 22.

[0057] Once the frame has been completed, the summed coincidence countdata is transmitted to the calculation processing unit 50, and forwardprojection of this data onto the projection data is carried out (S2-12).At this time, the pre-aligned projected mask is transmitted onto theprojection data in the calculation processing unit 50 from the imageinformation control unit 30. The projected PET data (projected radiationdata) and the projected mask are then composited in the calculationprocessing unit 50 (S2-13) Through this composition, the projected PETdata for the region of interest K is extracted, for example as shown inFIG. 7.

[0058] Next, in the calculation processing unit 50, PET data for theregion of interest K is obtained based on the extracted projected PETdata for the region of interest K (S2-14). This PET data for the regionof interest K is transmitted to the display unit 70, and is displayed asa graph or the like. Moreover, in the calculation processing unit 50, asin the first embodiment, the optimum administration rate such that theradiation concentration for the region of interest K will be steady iscalculated based on the PET data for the region of interest K (S2-15).

[0059] Afterwards, information on the calculated optimum administrationrate is transmitted to the administration rate control unit 60, and theadministration rate control unit 60 carries out feedback control suchthat the administration rate of the labeled substance T in theintravenous injection unit 40 becomes the optimum administration rate(S2-16). Once the above sequence of processing has been completed, themeasurement progresses to the next frame. During the measurement for thenext frame, the intravenous injection unit 40 administers the labeledsubstance T into the subject S at the calculated optimum administrationrate.

[0060] According to the PET apparatus 2 of the present embodiment,because compositing is carried out of the projected radiation data forthe region of interest K and the projected mask on the projection data,it becomes possible to improve the temporal resolution.

[0061] Finally, a description will be given of a third embodiment of thepositron emission tomography apparatus (PET apparatus) according to thepresent invention. The constitution of the PET apparatus 3 according tothe third embodiment is very similar to that of the first embodiment,and hence here a description will be given of the operation of the PETapparatus 3 with reference to the flowchart shown in FIG. 8, focusing inparticular on the region-of-interest data extraction processing, theadministration rate calculation processing and the administration ratecontrol processing.

[0062] Before describing the processing carried out after commencingmeasurement, a description will be given of processing carried outbefore commencing measurement. In this pre-measurement processing, PETmeasurement is carried out in advance on the measurement-subjected partH of the subject S (S3-1). A PET image is then reconstructed based onthe PET data obtained through this preliminary PET measurement (S3-2).

[0063] Moreover, as in the first embodiment, an MRI anatomical image orthe like of the measurement-subjected part H of the subject S that hasbeen measured in advance is inputted into the image information memory31 of the image information control unit 30, and the region of interestK is set on this image (S3-3). Next, a mask image that leaves behindonly the data for the region of interest K is created based on the setimage (S3-4), and then the mask image and the preliminary PET image arecomposited (S3-5).

[0064] Next, based on the composited image, the contribution rate toeach detector pair from the region of interest K is calculated (S3-6).This contribution rate is the proportion contributed by the radiationgenerated from the region of interest K out of the coincidence countvalue detected by the detector pair in question; for example, in thecase shown in FIG. 9, a value between 0 and 1 is set for each detectorpair based for example on the distance for which the line segmentjoining the pair of detectors cuts through the region of interest K oron the radiation concentration distribution obtained from thepreliminary PET image. A contribution rate table in which are collatedthe contribution rates for the respective detector pairs is then created(S3-7).

[0065] After the pre-measurement processing has been carried out asdescribed above, measurement is commenced. The measurement-subjectedpart H of the subject S is inserted into the measurement space of thedetection unit 10, and administration of the labeled substance T intothe subject S is commenced. Coincidence counting of the radiationgenerated from the measurement-subjected part is then carried out(S3-11). In the present embodiment, the coincidence count data obtainedis transmitted to the calculation processing unit 50 not frame by framebut rather in time series fashion. In the calculation processing unit50, the detector pairs that detected the coincidence count data areidentified (S3-12).

[0066] At this time, the contribution rate table for the detector pairswhich has been created in advance is transmitted to the calculationprocessing unit 50, and based on this the coincidence count data issubjected to weighting processing (S3-13). For example, in the case thatthe detection was by a detector pair for which the contribution rate is0.7 (70%), a coincidence count of 1 is reduced to 0.7. Note that, atthis time, a contribution rate table including the coincidence countdata obtained may be newly created, with this being used when the nextcoincidence count data is subjected to the weighting processing.

[0067] Next, in the calculation processing unit 50, PET data for theregion of interest K is extracted (S3-14) based on the coincidence countdata that has been weighted as described above. This PET data for theregion of interest K is transmitted to the display unit 70, and isdisplayed as a graph or the like. Moreover, in the calculationprocessing unit 50, as in the first embodiment, the optimumadministration rate such that the radiation concentration for the regionof interest K will be steady is calculated based on the PET data for theregion of interest K (S3-15).

[0068] Afterwards, information relating on the calculated optimumadministration rate is transmitted to the administration rate controlunit 60, and the administration rate control unit 60 carries outfeedback control such that the administration rate of the labeledsubstance T in the intravenous injection unit 40 becomes the optimumadministration rate (S2-16). In the present embodiment, the PET imagingprogresses to the next frame once one frame has been completed. However,the calculation and control of the optimum administration rate iscarried out as appropriate independently of the frame, and hence theintravenous injection unit 40 administers the labeled substance T to thesubject S at the optimum administration rate for the time in question.

[0069] According to the PET apparatus 3 of the present embodiment,because time-series-type data based on each of the detector pairs isused, it becomes possible to extract radiation data for the region ofinterest K with an extremely high temporal resolution.

[0070] The positron emission tomography apparatus (PET apparatus)according to the present invention is not limited to the aboveembodiments, with it being possible to adopt various modifications inaccordance with other conditions and so on. For example, in the aboveembodiments, the functions of the region-of-interest data extractionmeans for carrying out processing to extract the radiation data for theregion of interest K, and the functions of the administration conditioncalculation means for carrying out processing to calculate the optimumadministration condition are realized using a single calculationprocessing unit 50. However, a constitution is also possible in whichthese pieces of processing are carried out by processing units providedseparately via signal lines, i.e. by a region-of-interest dataextraction processing unit and an administration condition calculationprocessing unit respectively.

INDUSTRIAL APLICABLILITY

[0071] As described above, the positron emission tomography apparatus(PET apparatus) according to the present invention can be used as apositron emission tomography apparatus that enables measurements to becarried out easily and precisely, and also enables measurement resultsto be grasped rapidly and easily.

[0072] That is, it is no longer necessary to broaden the radiationconcentration measurement range of the PET apparatus, and moreover itbecomes possible to obtain the amount of change and so on in theradiation concentration for a region of interest between before andafter administration of a drug being tested easily and precisely in realtime. Sampling of arterial blood and complex numerical analysis are thusunnecessary, and hence great cutbacks can be made in the staff, time,analytical equipment and so on required for calculating the experimentalresults.

1. A positron emission tomography apparatus, which administers a positron-emitting labeled substance into a subject, and also carries out coincidence counting of radiation generated in a measurement-subjected part of said subject accompanying electron-positron pair annihilation, and measures the spatial distribution of the radiation concentration in said measurement-subjected part, characterized by comprising: region-of-interest data extraction means for extracting radiation data for a specified region of interest from out of the radiation data that has been obtained by coincidence counting from said measurement-subjected part; administration condition calculation means for calculating an optimum administration condition for said labeled substance into said subject based on the extracted radiation data for said region of interest; and administration control means for carrying out feedback control of an administration condition for said labeled substance into said subject based on said optimum administration condition.
 2. The positron emission tomography apparatus according to claim 1, characterized by further comprising region-of-interest data display means capable of instant image display of the extracted radiation data for said region of interest.
 3. The positron emission tomography apparatus according to claim 1 or 2, characterized in that said region-of-interest data extraction means sets said region of interest on an image in which positional information on said measurement-subjected part is displayed; creates a radiation data image by carrying out image reconstruction of the radiation data that has been obtained by coincidence counting from said measurement-subjected part, and a mask image in which radiation data for a region other than said region of interest is eliminated from said image, and extracts radiation data for said region of interest by compositing said radiation data image and said mask image.
 4. The positron emission tomography apparatus according to claim 1 or 2, characterized in that said region-of-interest data extraction means sets said region of interest on an image in which positional information on said measurement-subjected part is displayed, creates a mask image in which radiation data for a region other than said region of interest is eliminated from said image, creates projected radiation data by projecting the radiation data that has been obtained by coincidence counting from said measurement-subjected part onto projection data, and a projected mask by projecting said mask image onto said projection data, and extracts radiation data for said region of interest by compositing said projected radiation data and said projected mask.
 5. The positron emission tomography apparatus according to claim 1 or 2, characterized in that said region-of-interest data extraction means sets said region of interest on an image in which positional information on said measurement-subjected part is displayed, carries out weighting of a plurality of pieces of coincidence count data detected from said measurement-subjected part based on the positional relationship between said region of interest and a line segment joining a detector pair that obtained each piece of said coincidence count data, and extracts radiation data for said region of interest based on said weighting. 